The present invention generally relates to signal compression techniques, and more particularly to a compression technique that includes dividing the source signal into sub-signals and then encoding each of the sub-signals.
Bit-plane compression of digital signals is a popular coding method for many multimedia applications. For example, bit-plane coding of audiovisual signals enables progressive and scalable transmission of these signals. Typically, an audio or a visual signal undergoes some type of a transform prior to bit-plane coding. Examples of such transforms include the Discrete Cosine Transform (DCT) or the Discrete Wavelet Transform (DWT).
After performing one of the above-described transforms, each bit-plane included in the signal is then scanned and coded starting with the Most-Significant-Bit (MSB) representation of the signal and ending with the Least-Significant-Bit (LSB). Therefore, if each of the transform coefficients is represented by n bits, there are n corresponding bit-planes to be coded and transmitted.
Depending on a particular fidelity criterion (e.g., maximum allowable distortion) or a bit-rate budget constraint, the coding of the signal may be limited to a particular bit-plane. This approach provides the progressive feature of bit-plane compression especially when the coding is taking place in real-time, which can be at the same time the signal is being transmitted. For signals coded off-line or prior to transmission, bit-plane coding results in an embedded and scalable bit-stream. This enables the sender to limit the transmission of the stream at or within a particular bit-plane in response to, for example, to network conditions such as available bandwidth.
Consequently, bit-plane compression, in general, provides a very Fine-Granular-Scalability (FGS) coding of the signal. Depending on the particular method used for coding the bit-planes, this granularity could be as fine as a single bit or as coarse as an entire bit-plane. Therefore, if a signal is bit-plane coded using n planes and a total number of b bits, the resulting compressed stream could include anywhere between n and b progressive representations of the original signal embedded in that stream.
The present invention is directed to a method for compressing a signal. The method partitions the signal into a plurality of sub-signals and codes each of the sub-signals according to a different coding technique. Further, the sub-signals either include different bit-planes or different bits from the same bit-plane of the signal.
The present invention is also directed to method for compressing a signal that determines a xe2x80x9cbest choicexe2x80x9d partition for the signal. The signal is partitioned into a plurality of sub-signals according to the xe2x80x9cbest choicexe2x80x9d partition and then codes the sub-signals. The xe2x80x9cbest choicexe2x80x9d partition is determined by defining a number of different partitions for the signal. Further, an entropy value for each of the partitions is calculated and the partition having a minimum entropy value is selected.
The present invention is also directed to a method for de-compressing a signal including sub-signals and partition information indicating how the signal was partitioned into sub-signals. The method includes decoding each of the sub-signals and then combining the sub-signals according to the partition information.